1. Field of the Invention
The invention relates to a light emitting device, more particularly to a light emitting device for vehicles.
2. Description of the Related Art
Motor vehicles or motorcycles are generally installed with a lamp set, which is controlled by a power relay, at each of right and left sides on the rear of a vehicle body for providing indication when changing directions. Furthermore, for driving safety, another lamp set is installed at the rear of the vehicle body to provide indication when brakes are applied.
In a conventional motor vehicle provided with a single lamp unit, which includes a set of light emitting elements connected in parallel, for selectively providing indication when changing directions or when brakes are applied, a DC power, such as 12.8V, is supplied to the lamp unit for braking indication, whereas an AC power is supplied to the lamp unit via a power relay for direction indication. It is noted that the power relay must correspond to an equivalent impedance of the lamp unit in order to ensure normal flashing of the lamp unit at a predetermined frequency of 1-2 Hz. If one light emitting element of the lamp unit is broken, the equivalent impedance is increased so that the power relay enables the lamp unit to flash at a frequency higher than the predetermined frequency, such as 3-5 Hz, thereby altering the vehicle driver to repair the lamp unit. With such a construction, when the design conditions of the lamp unit, such as the number of the light emitting elements and the arrangement of the light emitting elements, are changed, it is necessary to provide an impedance matching element so as to maintain the equivalent impedance. It is noted that, due to the presence of the impedance matching element, heat generated thereby during a braking operation can result in damage to other elements. For example, the impedance matching element is usually mounted in the vicinity of a light casing made of an ABS material such that the light casing might melt when heat generated by the impedance matching element reaches about 90° C.